Phosphors for infrared-to-visible conversion

A zinc-incorporated phosphor for infrared-to-visible conversion, prepared by the process which comprises adding zinc fluoride in an amount of at least 2% by weight or zinc silicofluoride in an amount of at least 10% by weight based on the total weight of the anhydrous rare earth fluorides shown by the general composition hereafter, prior to or after formation of the main ingredient of the phosphor consisting essentially of a complex rare earth fluoride having a general composition expressed by one of the following formulae

• (Y.sub.1-x-y Yb.sub.x A.sub.y) F.sub.3, (La.sub.1-x-y Yb.sub.x A.sub.y) F.sub.3
• and
• (Lu.sub.1-x-y Yb.sub.x A.sub.y) F.sub.3,
• wherein x is in the range of from 0.05 to 0.5, y is in the range from 0.002 to 0.09 when yttrium fluoride is the host material and from 0.001 to 0.1 when lanthanum or lutetium fluoride is the host material, and A is at least one member selected from Er and Ho, and subsequent heating at a temperature ranging from 800.degree. to 1,200.degree. C when lanthanum fluoride is the host material and from 800.degree. to 1100.degree. C, when yttrium fluoride or lutetium fluoride is the host material for a time of 30 minutes to 5 hours in a neutral or anhydrous hydrogen fluoride atmosphere.